import java.util.Scanner;

public class Main {
    public static int Sum(int n){
        if(n<=1){
            return 1;
        }else {
            return Sum(n-1)+n;
        }
    }

    public static void main(String[] args) {
        Scanner num = new Scanner(System.in);
        while(num.hasNextInt()){
            int a = num.nextInt();
            System.out.println(Sum(a));
        }
    }
}
